This invention relates to a digital type time error measuring device for watches.
With conventional digital type time error measuring devices, manual selective operations must be carried out, so as to adapt them for optimum measuring accuracy which varies depending upon the type of the watch and the stepping or the like operating frequency.
It should be mentioned at this stage of description that the term "stepping" which is best applied to mechanical watches will be used also in reference to semi- or pure electronic watches.
There are generally three categories of watches. The first one is the traditional mechanical watch. The second one is the electro-mechanical watch, such as electromagnetically vibration or oscillation-sustaining tuning fork or drive balance wheel type, pulse motor-driven. The third one is the purely electronic and digital time display type.
When a watch is tested on a test bed for detecting the occasional time display error thereof, the stepping information of the watch must be derived for comparison with a standard clock pulse information developed and maintained by a separate generating source, such as a quartz oscillator built-in in the test bed.
In the case of a mechanical watch placed on the test bed the stepping movement of the balance wheel can be sensed by a mechanical sensor such as a bar feeler which is kept in contact with the watch case, and then converted into a corresponding electrical pulse series through a piezoelectric element mounted on the feeler.
In the case of a semi-electronic watch of tuning fork type as an example, being placed on the test bed, the required stepping information of the watch can be derived from drive coil means thereof and in the form of a stepping-responsive stray magnetic information which may converted into a corresponding electrical pulse series preferably by a sensing coil provided in the test bed.
Even if the watch is of the pulse motor drive type, the stepping-responsive magnetic information can equally be derived from the drive coil of the motor.
In the case of a pure electronic watch placed on the test bed, the required stepping-responsive information can be derived from the digital display electrode means and in the form of a periodically variable stray electrical field which can be converted into a corresponding electric pulse series by means of a sensing electrode provided in the test bed and acting as a counter electrode relative to said display electrode means, constituting thereby a capacitor in combination.
The aforementioned three categories of the watch correspond substantially to the stepping precision from low, for mechanical movements to high for electronic ones. Therefore, for carrying out measurements of time errors of watches, these watches must optimumly be classified into specific classes of measuring ranges. For this purpose, manual change-over manipulations have been carried out in use of the conventional test bed to adopt and select a most proper measuring range among various ranges provided in the test bed.